[Bug 1910273] Re: Upgrade to groovy breaks DNS resolution

[falstaff]

*** This bug is a duplicate of bug 1907878 ***
    https://bugs.launchpad.net/bugs/1907878

I've run into the same problem on a server upgraded from 18.04 to 20.04
and 22.04. After the last upgrade step, DNS did not work anymore. It
seems that DNS information does not get properly propagated from
ifupdown configuration (/etc/network/interfaces) to systemd-resolved.

The main issue seems to be this error:
```
/etc/network/if-up.d/resolved: 70: DNS: not found
```

It seems that the state files e.g. /run/network/ifupdown-inet-eth0 contain the following string:
```
"DNS"="<ip-of-dns>"

When the script tries to source the file around line 78, this fails. I
fixed it by removing the quotes around $DNS and $DOMAINS on line 47 and
51.

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https://bugs.launchpad.net/bugs/1910273

Title:
  Upgrade to groovy breaks DNS resolution

Status in ifupdown package in Ubuntu:
  Confirmed

Bug description:
  ~# lsb_release -rd
  Description:	Ubuntu 20.10
  Release:	20.10
  ~# apt-cache policy ifupdown
  ifupdown:
    Instalēts: 0.8.35ubuntu2
    Kandidāts: 0.8.35ubuntu2
    Versiju tabula:
   *** 0.8.35ubuntu2 500
          500 http://mirrors.digitalocean.com/ubuntu groovy/universe amd64 Packages
          100 /var/lib/dpkg/status
  ~#

  Problem: Upon upgrade from Ubuntu 20.04 to Ubuntu 20.10, I expected
  name resolution upon reboot to work as usual.

  What happened:
  a) /var/log/syslog sprinkled with error messages:
  - /etc/network/if-up.d/resolved: 12: mystatedir: not found
  - /etc/network/if-up.d/resolved: 70: DNS: not found
  - /etc/network/if-up.d/resolved: 1: /run/network/ifupdown-inet-eth0: DNS=8.8.8.8 8.8.4.4: not found
  b) resolvectl dns returning no name servers

  Investigation:
  Recently changed /etc/network/if-up.d/resolved and /etc/network/if-down.d/resolved files contain programming errors. See https://git.launchpad.net/ubuntu/+source/ifupdown/commit/?id=54fec5eedfd59adaffe9021c271914578dd05d1b .

  Fix:
  $ diff /Users/pklavins/Downloads/ifupdown-0.8.35ubuntu2/debian/if-down.d/resolved if-down.d_resolved 
  12c12
  <     mystatedir statedir ifindex interface
  ---
  >     # local mystatedir statedir ifindex interface
  $ diff /Users/pklavins/Downloads/ifupdown-0.8.35ubuntu2/debian/if-up.d/resolved if-up.d_resolved 
  12c12
  <     mystatedir statedir ifindex interface
  ---
  >     # local mystatedir statedir ifindex interface
  39,40c39,40
  <     DNS=DNS
  <     DOMAINS=DOMAINS
  ---
  >     DNS=$DNS
  >     DOMAINS=$DOMAINS
  42,43c42,43
  <         DNS=DNS6
  <         DOMAINS=DOMAINS6
  ---
  >         DNS=$DNS6
  >         DOMAINS=$DOMAINS6
  47c47
  < "$DNS"="$NEW_DNS"
  ---
  > DNS="$NEW_DNS"
  51c51
  < "$DOMAINS"="$NEW_DOMAINS"
  ---
  > DOMAINS="$NEW_DOMAINS"
  70c70
  <         DNS DNS6 DOMAINS DOMAINS6 DEFAULT_ROUTE
  ---
  >         # local DNS DNS6 DOMAINS DOMAINS6 DEFAULT_ROUTE
  $

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